Fairground palmists who claim to tell your age could soon be out of work. Just 22 metabolites in the blood can now be used to estimate age from a single blood test, and possibly even reveal early signs of diseases associated with ageing. According to Tim Spector at King's College London, until now the only recognised biological indicator of age has been the length of telomeres – tips of chromosomes that wear down each time a cell divides, and so which shorten with age. Now Spector and his team have identified a panel of 22 metabolites – small molecules such as fats and amino acids – that vary over time and can be used to reveal age to within 10 years.